Multi-disc damper using viscous fluid

ABSTRACT

A damper comprising within a casing filled with viscous fluid a number of movable discs to be moved in response to the transmitted external force and a number of not interlocked fixed discs arranged in an alternative arrangement, wherein both movable and fixed discs are axially deflectable can maintain even clearances between the movable and the fixed discs due to the alignment effect of the discs without undergoing unreasonable stress that can damage the discs. The allowable limit of deflection of the fixed and movable discs can be made adjustable so as to modify the total drag of the damper. Sources of resilient restoring force may be provided to enhance the capability of adjustment. Moreover, the number or the size of the movable and/or the fixed discs can be made alterable to effectively modify the drag of the damper.

FIELD OF TECHNOLOGY

This invention relates to a damper using a high-molecular viscous fluidmaterial such as polyisobutylene with a view to utilize its high viscousdrag against shearing force for buffering or damping the external force,thereby providing a variety of potential applications.

TECHNICAL BACKGROUND

It is well known that a conventional damper utilizes the turbulence ofthe oil it contains to absorb the shock imparted by an external force.Such turbulence occurs when the oil passes through narrow slits providedwithin the damper as oil is pressed by the external force.

However, with such a damper, high precision is required for the make ofthe slits to accurately generate a required resisting force in order toaccurately produce the required damping effect. Morever, as oil cannotbe compressed when a strong external force is abruptly applied to it,the external force is apt to be directly received by the strucuralmembers the damper is supposed to protect. To overcome this problem, adamper is normally designed to have an excessively high strength againstexternal force, making in turn its overall size very bulky. Besides, theslits are liable to become narrow as dust and other foreign matters arecaught by the slits and eventually clogged to completely block the flowof oil.

In order to eliminate these disadvantages of the damper of theconventional designa as described above, an improved damper has beenproposed, which basically comprises two independent solid membersarranged in such a manner that they are movable relative to each otherand have surfaces located vis-a-vis and close to each other and a highlyviscous liquid material filled therebetween so that it can provideresistance against external force due to the viscous drag of the liquidmaterial against shearing force that can be generated without raisingthe internal pressure of the liquid when an external force is appliedthereto.

A typical damper which was realized in relatively early days on thebasis of this design a concept comprises a casing in which a certainnumber of movable discs are radially and perpendicularly fitted to arotary shaft and a same number of fixed discs are fitted to the casingin such a manner that the movable discs and the fixed discs are arrangedalternatively with an appropriate clearance between any two adjacentdiscs and the oil which is contained within the casing fills the spacesbetween the discs.

With a damper having a configuration as described above, when anexternal force is applied to the rotary shaft, the movable discs fittedthereto and the fixed discs fitted to the casing are caused to moverelative to each other and the viscous liquid filling the spaces betweenthe discs generates viscous drag against the shearing action of theexternal force to bring forth the overall effect of the damper. However,with such an arrangement, the distance between the two adjacent discshas to be precisely identical for all the discs. If not, the portion ofthe viscous fluid found between a pair of discs having a relativelysmall clearance generates a larger viscous drag than the portion of thefluid found between a pair having a relatively large clearance, causingan unreasonably large stress to occur in the are having a large viscousdrag that can eventually damage the damper, since the discs are rigidlyfitted either to the casing or the rotry shaft and the clearance betweena pair of adjacent discs and are not adjustable.

Consequently, manufacture of such a damper requires a considerable highprecision. Moreove, such a damper is not capable of altering its dampingeffect by altering the surface area of the discs because they arerigidly fitted to the supporting members and not accessible fromoutside, while the amount of viscous drag is proportional to the surfacearea of the adjacent discs which are facing to each other. This meansthat if a damper having a different damping effect is needed, acompletely new damper has to be provided.

In order to eliminate the drawbacks of the above described damper of theearly days, a rotational damper using a plurality of discs and a viscousfluid material has been proposed (Japanese Utility Publication No.57-39664). FIGS. 22a and 22b illustrate a damper according to thedisclosed utility design.

This damper comprises, as in the case of the above described damper ofthe early days, cylindrical casing a having rotatable shaft c along itslongitudinal axis which is rotated when an external force is applied toa pivotable arm b fitted to said rotatable shaft c. A plurality ofmovable discs d, d, . . . are arranged radially and perpendicularly tosaid rotary shaft c and rigidly fitted thereto by welding or some othermeans, while a plurality of fixed discs e, e, . . . are fitted to casinga not rigidly but through engagement of grooves f, f, . . . of saidfixed discs e, e, . . . and a pair of longitudinal ridges g, g so thatwhile fixed discs e, e, . . . are blocked against rotating movement,they can be deflected in the axial direction of the damper within acertain limit as most clearly seen in FIG. 22(a). The space withincasing a is filled with viscous fluid as in the case of the damperdescribed earlier.

This improved damper is advantageous in that it is free from any damageif an unreasonable force is applied from outside to fixed discs e, e, .. . in the axial direction, because said fixed disc e, e, . . . are soarranged that they can be axially deflected and thereby absorb theexternal force and that even when there is a fixed disc e which islocated significantly closer to one of its adjacent movable discs thanto the other and hence generates a viscous drag against shearing forcerelatively larger than the viscous drage generated between disc e andthe other adjacent movable disc as movable discs d, d, . . . arerotatingly moved relative to fixed discs e, e, . . . , said fixed disc eis automatically pushed away to come closer to the other adjacentmovable disc having a relatively small viscous drag between itself andsaid fixed disc e. By this action (so-called alignment effect), each offixed discs e, e, . . . always tends to take a position where it evenlydivides the space between two neighboring movable discs to generate aviscous drag which is equal to those generated by the rest of the fixeddiscs, thereby preventing any possible damages from occuring due toabnormally large viscous drags that are loacally generated.

However, this improved damper also has certain drawbacks. Firstly, sincemovable discs d, d, . . . are rigidly fitted to rotary shaft c, they arerequired to be located with high precision to ensure an evenlydistributed viscous drag. Secondly, since the distance between anyadjacent movable disc is not adjustable, the surface area of each fixeddisc e needs to be altered, if the magnitude of the overall viscous dragis required to be changed.

Therefore, alteration of the surface area of fixed disc e, e, . . . ispractically not feasible because such an operation requires dismantlingof the damper assembly and disengagement as well as reengagement of thefixed discs with axial ridges g, g. A completely different damper shouldbe provided to realize a viscous drag which is different from that ofthe original damper.

Moreover, since movable discs d, d, . . . are rigidly fitted to rotaryshaft c, alteration of the distance between any given movable disc d andthe adjacent disc e from outside is practically not feasible althoughsuch capability of alteration is indispensable for a damper that canmeet the practically requirement of adjusting its viscous drag within acertain limit.

Consequently, if a variable damping effect is required for a givenapplication, there have to be prepared a number of dampers havingdifferent damping effects that satisfy the requirements by providingcasings, movable discs and fixed discs with different sizes. With suchan arrangement, a damper having a large clearance between the adjacentmovable fixed discs or one having a relatively small surface area of themovable and fixed discs may be used if a small damping effect isrequired, whereas a damper having a small clearance between the adjacentmovable and fixed discs or one having a relatively large surface area ofthe movable and fixed discs may be used for a relatively small viscousdrag.

A damper of the type as described above is also accompanied by anothermajor drawback. Any viscous fluid material contained in the damper losesits vicosity and hence its viscous drag against shearing force to someextent as the ambient air temperature rises in summer, whereas itobtains an additional viscosity and hence an additional viscous drag tocertain extent in winter when the temperature falls. So, a damper thatoperates normally in winter can have a poor damping effect in summerand, if it is used as a door check, come to be a defective device thatcan not effectively absorb shocks and allow the door to bang when it isshut.

It is therefore an object (the first object) of the present invention toprovide a damper which is designed on the basis of a completely newconcept of using fixed discs and movable discs that can be axiallydeflected, a concept which is totally different from that of the abovedescribed conventional dampers comprising both fixed and movable discsrespectively rigidly fitted to a casing and a rotary shaft or axiallydeflectable fixed discs fitted to a casing and movable discs rigidlyfitted to a rotary shaft, where rigidly fitted members are involved inany case. According to this new concept, not only the fixed disc butalso the movable discs are so arranged that they can be axiallydeflected. Thus, when the movable discs are subjected to an externalforce in the form of rotation or traction so that they come to formclearances with their adjacent fixed discs having distances which aredifferent from one another, a flow of the viscous fluid occurs withinthe damper to bring forth the above-mentioned alignment effect (aneffect of viscous fluid to flow from areas where the viscous drag is lowto areas where the drag is high, or areas where the clearance ofadjacent discs is narrowed, to equalize the clearances) and equalize theclearance for all the discs. With such an arrangment, a damper which isfree from damage due to abnormally high local viscous drags can bemanufactured without requiring high precision.

It is another object (the second object) of the present invention toprovide a damper comprising deflectable fixed and movable discs asdescribed above by referring to the first object, said damper furtherhaving an axial total effective length that can be adjusted from outsidewithin a predetermined limit to alter the clearance of the adjacentdiscs and hence the overall damping effect of the damper rapidly andeasily.

It is a further object (the third object) of the present invention toprovide a damper as described above by referring to the second object,said damper further comprising resilient members capable of restoringthe axial total effective length of the damper when it is axiallycompressed to ensure a smooth initial action of the damper and an easyadjustment of its effects.

It is a still further object (the fourth object) of the presentinvention to provide a damper, unlike dampers as described above byreferring to the second and third objects and having a means foradjusting the viscous drag, comprising a means for altering the numberof movable discs which are rotated with a rotary shaft through anoperation conducted from outside to adjust the overall drag of thedamper and a means for replacing all the replaceable fixed and movablediscs with those having a different surface area easily and rapidly toalter the nominal viscous drag of the damper.

It is a still further object (the fifth object) to provide a dampercomprising axially deflectable fixed and movable discs whose clearancescan be easily altered simply by altering the axial total effectivelength of the damper from outside to adjust the overall drag of thedamper and a means for replacing the replaceable fixed and movable discswith those having a different surface area to alter the nominal drag ofthe damper, said damper further comprising a deformable feeler elementsensitive to temperature change within the casing at a location wheresaid element is effectively thermally deformed to automatically maintainthe predetermined level of drag of the damper regardless of temperaturechange without necessity of adjustment by operators.

It is a still further object (the sixth object) of the present inventionto provide a damper, unlike the one having a feeler element as describedabove by referring to the fifth object, comprising movable discs andfixed discs either or both of which are made of a thermally deformablematerial which is sensitive to temperature change to effectively utilizethe thermal deformation of the discs made of such a material to maintainthe predetermined level of drag of the damper regardless of temperaturechange without necessity of adjustment by operators.

It is a still further object (the seventh object), of the presentinvention to provide a damper comprising, is addition to the features ofthe one as described by referring to the fourth object, movable andfixed discs constantly under the effect of a resilient external force,either or both of said movable and fixed disc being made of a thermallysensitive and deformable bimetal to effectively utilize thermaldeformation of the bimetal to maintain the predetermined level of dragof the damper, regardless of temperature change without necessity ofadjustment by operators.

DISCLOSURE OF THE INVENTION

According to the present invention, the first object of the inventionisachieved by providing a damper comprising within a casing a number ofmovable discs arranged on a rotary shaft, said movable discs beingrotated or tracted in accordance with the rotary or tractive movement ofthe rotary shaft caused by external force, a number of fixed discsprovided in an alternative arrangement with said movable discs in such amanner that they are not interlocked with the rotary shaft for rotary ortractive movement and a viscous fluid material filling the space betweenthe movable and fixed discs, said damper being characterized by thatsaid fixed discs are engaged with the casing in such a manner that theyare not movable radially or in the direction of rotation or traction butaxially or longitudinally deflectable.

With such an arrangement, when the rotary shaft is subjected to a rotaryforce or a linear tractive force, the movable discs engaged or coupledwith the rotary shaft are rotated or tracted in the viscous fluid,thereby generating a viscous drag against shearing force of the fluidfound between the movable discs and the fixed discs which are notinterlocked with the rotary shaft for the movement of the movable discsto buffer the applied external force so that the assembly operates as adamper. At this stage, thanks to the alignment effect, a flow of theviscous fluid occurs toward the areas where the viscous drag againstshearing force is relatively high so that, if there are variations ofclearances between the movable and fixed discs, they are axially movedby the flow of the fluid that runs into the areas where the clearancebetween the movable disc and the fixed disc is small and hence theviscous drag against shearing force is high in such a manner that themovable and fixed discs are axially deflected to equalize all theclearances between the adjacent discs throughout the total effectivelength of the damper, thereby eliminating any abnormal conditions whereunreasonable drags are locally generated to damage the members of thedamper assembly.

The second object of the present invention is achieved by providing adamper comprising within a casing a number of movable discs arranged ona rotary shaft, said movable discs being rotated or tracted inaccordance with the rotary or tractive movement of the rotary shaftcaused by external force, a number of fixed discs provided in analternative arrangement with said movable discs in such a manner thatthey are not interlocked with the rotary shaft for rotary or tractivemovement and a viscous fluid material filling the space between themovable and fixed discs, said damper being characterized by that saidfixed discs are not radially movable because of the engagement with thecasing but axially deflectable, that the movable discs are also axiallydeflectable and that the axial total effective length of the damper canbe adjusted within a predetermined limit to alter the clearance of theadjacent movable and fixed discs by operating an adjusting member thatcan be operated from outside.

A damper as described above by referring to the second object of theinvention has not only an identical effect as a damper that achieves thefirst object, but also an effect of adjusting its damping capacity byaltering the axial total effective length of the damper by means of theadjusting member so that the total effective length and accordingly theclearance between the adjacent discs may be decreased to increase theviscous drag or increased to decrease the viscous drag.

The third object of the present invention is achieved by providing adamper comprising with a casing a number of movable discs arranged on arotary shaft, said movable discs being rotated or tracted in accordancewith the rotary or tractive movement of the rotary shaft caused byexternal force, a number of fixed discs provided in an alternativearrangement with said movable discs in such a manner that they are notinterlocked with the rotary shaft for rotary or tractive movement and aviscous fluid material filling the space between the movable and fixeddiscs, said damper being characterized by that said fixed discs are notradially movable because of the engagement with the casing but axiallydeflectable, that the movable discs are also axially deflectable, thatthe axial total effective length of the damper can be adjusted within apredetermined limit to alter the clearance of the adjacent movable andfixed discs by operating an adjusting member that can be operated fromoutside and that resilient members capable of restoring the axial totaleffective length of the damper when it is axially compressed provided toensure a smooth initial action of the damper and an easy adjustment ofits effects.

A damper as described above by referring to the third object of theinvention has not only an identical effect as a damper that achieves thesecond object, but also, thanks to the resilient members, and effect ofquickly restoring its original axial total effective length to increasethe clearance between the movable and fixed discs when the damper hasbeen axially compressed to decrease the axial effective length and thenreleased from the compressive force and of preventing the discs fromtotally losing their clearance even when the damper is left in an idlecondition without any external rotating force applied thereto andtherefore keeping its viscous fluid in a desired condition so that itcan smoothly exert its damping function whenever an external force isapplied thereto.

The fourth object of the invention is achieved by providing a dampercomprising within a casing a number of movable discs arranged on arotary shaft, said movable discs being rotated or tracted in accordancewith the rotary or tractive movement of the rotary shaft caused byexternal force, a number of fixed discs provided in an alternativearrangement with said movable discs in such a manner that they are notinterlocked with the rotary shaft for rotary or tractive movement and aviscous fluid material filling the space between the movable and fixeddiscs, said damper being characterized by that said fixed discs are notradially movably because of the engagment with the casing but axiallydeflectable, that the movable discs are also axially deflectable, thatsaid rotary shaft is provided with a locking portion having teeth thatcomes to engagement with movable discs and a nonlocking portion thatgoes through the bottom of the casing and that the rotary shaft is madeto be axially movable by means of a rotary adjusting member provided onthe bottom of the casing and coupled to said nonlocking portion so thatthe nonlocking portion goes into or comes out of the casing according tothe axial movement of the rotary shaft in such a manner that the movablediscs can come off from the locking portion one by one starting from theone situated closest to the nonlocking portion or inversely come intoengagement with the locking portion in accordance with the movement ofthe shaft.

A damper as described above by referring to the fourth object of theinvention has not only an identical effect as a damper that achieves thefirst object, but also an effect of significantly decreasing the drag ofthe damper that can be achieved by operating the rotary adjusting memberfrom outside to move the rotary shaft upward and accordingly thenonlocking portion thereof into the casing so that the movable discsituated closest to the nonlocking portion comes off from the lockingportion into the area of nonlocking portion and into a state where it isnot interlocked with the rotary shaft any more and loses its function asa source of viscous drag realized with the fixed disc locatedimmediately above it. In this manner the drag of the damper can begradually reduced by bringing the movable discs one by one out of thelocking portion. As a matter of course, the drag of the damper can beincreased by inversely bringing the idle movable discs one by one intoengagement with the locking portion.

The fifth object of the present invention is achieved by providing adamper comprising within a casing a number of movable discs arranged ona rotary shaft, said movable discs being rotated or tracted inaccordance with the rotary or tractive movement of the rotary caused byexternal force, a number of fixed discs provided in an alternativearrangement with said movable discs in such a manner that they are notinterlocked with the rotary shaft for rotary or tractive movement and aviscous fluid material filling the space between the movable and fixeddiscs, said damper being characterized by that said fixed discs are notradially movable because of the engagement with the casing but axiallydeflectable, that the movable discs are also axially deflectable andthat one or more than one deformable feeler elements are provided at thebottom of the casing or between the movable and fixed discs, saiddeformable feeler elements being deformed to push up the discs so thatthe clearance between the movable and fixed discs is narrowed whentemperature rises within the casing and inversely to lower the discs sothat the clearance is widened when temperature falls.

A damper as described above by referring to the fifth object of theinvention has not only an identical effect as a damper that achieves thefirst object, but also an effect of compensating any reduction of thedrag of the damper caused by the decreased viscosity due to atemperature rise in summer through deformation of the feeler element tonarrow the distance between the adjacent movable and fixed discs,thereby eliminating the drawback of fluctuation of the drag in responseto the fluctuation of ambient temperature.

The sixth object of the present invention is achieved by providing adamper comprising within a casing a number of movable discs arranged ona rotary shaft, said movable discs being rotated or tracted inaccordance with the rotary or tractive movement of the rotary shaftcaused by external force, a number of fixed discs provided in analternative arrangement with said movable discs in such a manner thatthey are not interlocked with the rotary shaft for rotary or tractivemovement and a viscous fluid material filling the space between themovable and fixed discs, said damper being characterized by that saidfixed discs are not radially movable because of the engagement with thecasing but axially deflectable, that the movable discs are also axiallydeflectable and that all or part of both or either of the movable discsand the fixed discs are made of a material which is deformed with changeof temperature to narrow the clearance between the movable and fixeddiscs when temperature rises and inversely to widen the clearance whentemperature falls.

A damper as described above by referring to the sixth object of theinvention has not only an identical effect as a damper that achieves thefirst object, but also as in the case of a damper that achieves thefifth object an effect of compensating any reduction of the drag of thedamper caused by the decreased viscosity due to a temperature rise insummer through expanding deformation of both or either of the movablediscs and the fixed discs to narrow the distance between the adjacentmovable and fixed discs, thereby eliminating the drawback of fluctuationof the drag in response to the fluctuation of ambient temperature.

The seventh object of the present invention is achieved by providing adamper comprising within a casing a number of movable discs arranged ona rotary shaft, said movable discs being rotated or tracted inaccordance with the rotary or tractive movement of the rotary shaftcaused by external force, a number of fixed discs provided in analternative arrangement with said movable discs in such a manner thatthey are not interlocked with the rotary shaft for rotary or tractivemovement and a viscous fluid material filling the space between themovable and fixed discs, said damper being characterized by that saidfixed discs are not radially movable because of the engagement with thecasing but axially deflectable, that the movable discs are also axiallydeflectable, that the movable and fixed discs are constantly subjectedto a resilient external force tending to narrow the clearance betweenthe movable and fixed discs and that both or either of the movable discsand fixed discs are made of a bimetal which is deformed with change oftemperature to widen the clearance between the movable and fixed discsagainst said resilient external force when temperature falls andinversely to narrow the clearance under the influence of said resilientexternal force when temperature rises.

A damper as described above by referring to the seventh object of theinvention has not only an identical effect as a damper that achieves thefirst object, but also an effect of reducing the degree of the rise ofthe drag due to the increase of the viscosity of the viscous fluidcaused by temperature fall in winter because of deformation of thebimetal to widen the clearance between the movable and fixed discs andof increase of the total effective length of the damper that allowsaxial adjustment of the movable and fixed discs and compensating thedecrease of the viscosity of the viscous fluid caused by temperaturerise in summer because of restoration of the original shape of the discsof bimetal to shorten the total effective length of the damper and tonarros the clearance between the adjacent movable and fixed discs,thereby eleiminating any abnormal conditions that may be caused to thedanger by abrupt changes of ambient temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a longitudinal sectional front view showing the principalpart of an embodiment of the rotary damper according to the presentinvention designed to achieved its first object.

FIG. 1b is an exploded perspective view of the embodiment of FIG. 1a.

FIG. 1c is a perspective view of the embodiment of FIG. 1a, illustratingthe stage where it is almost assembled.

FIGS. 2 and 3 are exploded perspective views similar to FIG. 1b showingtwo other embodiments designed to achieve the 1st object of theinvention.

FIG. 4a is a longitudinal sectional view showing the principal part ofan embodiment of the traction damper according to the invention.

FIG. 4b is an exploded perspective view of the embodiment of FIG. 4a.

FIG. 5a is a partial sectional front view of an embodiment using fixeddiscs of different design.

FIG. 5b is a partial sectional front view of an embodiment using ringspacers.

FIG. 5c is a plan view showing a disc of different design.

FIG. 5d is a partial sectional front view illustrating anotherembodiment.

FIG. 6a is a longitudinal sectional front view showing the principalpart of an embodiment of the rotary multi-disc damper according to thepresent invention designed to achieve its second object.

FIG. 6b is an exploded perspective view of the embodiment of FIG. 2a.

FIG. 7 is a longitudinal sectional from view showing the principal partof an embodiment of the rotary multi-disc damper according to thepresent invention designed to achieve its third object.

FIG. 8a is a longitudinal sectional view illustrating a movable disc ofthe embodiment of FIG. 7.

FIGS. 8b and 8c are longitudinal sectional views illustrating twomovable discs to be used for two other embodiments.

FIGS. 9a and 9b are respectively a longitudinal sectional front view andan exploded perspective view showing another embodiment of the rotarymulti-disc damper according to the invention designed to achieve thesecond object of the invention but different from the embodiment ofFIGS. 6a and 6b.

FIG. 10 is a longitudinal sectional front view showing the principalpart of an embodiment of the rotary multi-disc damper according to thepresent invention designed to achieve its fifth object.

FIG. 11 is an exploded perspective view of the embodiment of FIG. 10.

FIGS. 12a and 12b are longitudinal sectional front views showing twoother embodiments of the damper according to the present inventiondesigned to achieve its fifth object.

FIGS. 13a and 13b are exploded perspective views respectivelyillustrating the embodiments of FIGS. 12a and 12b.

FIGS. 14a, 14b and 14c are longitudinal sectional front views of threedifferent embodiments of the damper according to the present inventiondesigned to achieve its sixth object.

FIGS. 15a, 15b and 15c are exploded perspective views respectivelyillustrating the embodiments of FIGS. 14a, 14b and 14c.

FIG. 16 is a longtudinal sectional front view showing the principal partof an embodiment of the damper according to the present inventiondesigned to achieve its seventh object.

FIG. 17 is an exploded perspective view of the embodiment of FIG. 16.

FIGS. 18, 19 and 20 are longitudinal sectional front views of threeother embodiments.

FIGS. 21a and 21b are schematic front views illustrating the inside ofthe damper of FIG. 16 respectively when ambient temperature is high andwhen temperature is low.

FIGS. 22a and 22b are respectively a longitudinal sectional front viewand a lateral sectional view of a conventional damper using viscousfluid.

DESCRIPTION OF PREFERRED EMBODIMENTS

A number of embodiments of the damper according to the inventiondesigned to achieved its first object are illustrated in FIGS. 1athrough 5d. of which FIGS. 1a through a 3 are illustrations ofembodiments comprising plurality of movable and fixed discs, FIGS 4a and4b are illustrations of an embodiment of traction type and FIGS. 5athrough 5d are illustrations of embodiments of rotary type designed toprevent an undesired flow of viscous fluid in a stationary condition anfto urge a smooth flow of the fluid in an operating condition.

Now referring to the embodiment of FIGS. 1a through 1c of the rotarymulti-disc damper, cylindrical casing 1 is provided with bearing recess1b at the bottom 1a and symmetrically arranged vertical grooves 1d, 1d,. . . on an inner surface 1c.

A rotary shaft 2 is rotatably arranged along the longitudinal axis ofsaid casing 1 and its front end is engaged into said bearing recess 1b,while cover plate 3 is screwed into the upper threaded portion 1e , ofthe casing 1 from above a flange 2a provided on the upper section of therotary shaft 2 so that a squared top portion 2c located above the flange2a and provided with coupling threaded bore 2b from said cover plate 3.

The projecting section of said squared top portion 2c comes intoengagement with a square bore 4b of a rotary arm 4 which is subjected toexternal turning force. A holder screw 5 comes into engagment withcoupling threaded bore 2b to hold said arm 4 against disengagement.

The casing 1 which is sealed by a cover plate 3 contains viscous fluid Aof a viscous high-molecular material such as polyisobutylene or otherviscous material such as pitch or sticky water glass as well as movaablediscs 6, 6, . . . and fixed discs 7, 7, . . . which are vertically andalternatively arranged in a manner as described below.

Movable disc 6 is a disc having a central opening 6a that comprisesnotches 6b, 6b, . . . which come into engagement with ridges 2d, 2d, . .. provided vertically on the lateral surface of said rotary shaft 2 sothat said movable disc 6 rotates with rotary shaft 2 and can slidinglymove in the axial direction or, in FIG. 1a, upward or downward.

The fixed disc 7 has a circular opening 7a at the center andsymmetrically arranged holder projections 7b, 7b, . . . on itscircumference. Since the rotary shaft 2 idly runs through opening 7a,the turning movement of rotary shaft 2 is not transmitted to fixed disc7. Moveover, since said holder projections 7b, 7b, . . . are engagedwith vertical ridges 1d, 1d, . . . of casing 1, it is not affected bythe turning force or turbulence of the viscous fluid, while it can beslidingly moved in the axial direction like movable disc 6. Referencesymbol 3a denotes a central bore of the cover plate 3 for receiving therotary shaft.

Now suppose that a rotary damper as described here is used as a doorcheck. When an external turning force is applied to the rotary arm 4,the rotary shaft 2 and accordingly movable discs 6, 6 . . . turn inresponse. This movement generates a viscous drag against shearing forcewithin viscous fluid A found in the clearances between the discs, which,along with the alignment effect as described earlier, deflects the discaxially in such a manner that all the clearances between the discs tendto be equalized. Consequently, the discs within the casing are arrangedparallel to each other to evenly divide the total effective length ofthe casing 1.

Now referring to the embodiments illustrated in FIGS. 5a through 5d, ofwhich FIG. 5a shows an embodiment using the fixed disc 7 havingthickened circumferential portion 7c while FIG. 5b shows an embodimentusing a ring spacer RS between fixed disc 7 and movable disc 6, theseembodiments being provided with a preventive measure against fallingdown of the discs due to their own weight while they are not in use.Otherwise, all the viscous fluid will be pushed away to move into theouter space of the discs as the discs fall down and the viscous dragagainst shearig force will not be effectively and rapidly generatedwithin the viscous fluid when an external force is applied to thedamper.

FIG. 5c shows an embodiment where arc-shaped slits 6c, 6c are formed onmovable disc 6, which accelerate the flow of viscous liquid from thecircumferential area to the central area of the casing when the disc isturned in the direction of the arrow with rotary shaft 2 in order toensure a smooth movement of viscous liquid A among the discs. FIG. 5dillustrates an embodiment where a relatively large central bore 7a ofthe fixed disc 7 and the movable disc 6 having a relatively small outerdiameter are realized to enhance the mobility of viscous fluid A inorder to ensure a rapid substantiation of the alignment effect.

FIGS. 2 and 3 illustrate two other embodiments, of which the embodimentof FIG. 2 has a configuration for the rotray shaft and the relatedcomponents with differs from that of FIG. 1 in the following manner.

Namely, in this embodiment, rotary shaft 2 is not realized in one-piecebut actually a collection of central shaft 2e and eccentric shaft 2f,2f, which are separately and respectively held in opening 6d for centralshaft 2d and openings 6e, 6e for eccentric shafts 2f, 2f correspondingcollectively to central opening 6a of the embodiment of FIG. 1.Therefore, the turning movement of rotary shaft 2 is transmitted to themovable disc 6 by means of these three shafts. Circular opening 7a offixed disc 7 of this embodiment has a diameter large enough to looselyand collectively accomodate a central shaft 2e and eccentric shafts 2f,2f.

The embodiment of FIG. 3 also has a configuration for rotary shaft 2 andthe related components which are different from its counterparts in theother embodiments. In this embodiment, a rotary shaft 2 has notches 2h,2h, . . . on the periphery of a flange 2a formed on a shaft body 2gcomprising squared top portion 2c. These notches come into engagementwith teeth 6f, 6f, . . . standing upward from the circumference of thecentral opening of the uppermost movable disc 6, while notches 6g, 6g, .. . provided between teeth 6f, 6f, . . . and standing upward from thecircumference of the central opening of the movable disc 6 immediatelybelow the uppermost disc 6 come into engagement with teeth 6f, 6f, . . .of the movable disc 6 immediately below said second disc 6. In a similarmanner, a number of movable discs are engaged with one another so thatthe turning movement of shaft main body 2g is successively transmitteddown to the lowermost movable disc. Needless to say, teeth 6f, 6f, . . .are realized with such dimensions and form that the teeth can freelypass through circular opening 7a of fixed disc 7.

Whereas the above embodiments are designed to receive external rotatingforce, the embodiment in FIGS. 4aand 4b is designed to generate aviscous drag against shearing force when an external force is applied torotary shaft 2 to tract it in the linear direction.

In this embodiment, casing 1 comprises main body 11a and an auxiliarybody 11b to be held by the two lateral edges of the main body and athreaded cap 11e to be screwed on the mouth portion of the casing whenmouth halves 11c, 11d formed respectively on the top of bodies 11a, 11bare put together. Said threaded cap 11e has shaft bearing bore 11fformed in the centre, by which movable shaft 2 is slidably held. A joint2j is pivotably fitted to the end of a rotary shaft 2 in the casing 1 bymeans of a shaft pin 2i as shown in FIG. 4a.

Said joint 2j comprises a pair of bearing pieces 2k, 2k and horizontalpiece 21 that connects them. A guide pin 2m is horizontally carried bysaid bearing pieces 2k, 2k at the lower portion thereof and movableplate 6, 6, . . . are suspended from said guide pin as it runs through aguide holes 6h provided on the upper portion of each movable plate 6.With such an arrangement, movable plates 6, 6 . . . can be deflectedlaterally, or either to the right or to the left of the drawing.

Fixed plates 7, 7, . . . are provided in casing 1 in an alternativearrangement with movable plate 6, 6, . . . In these embodiments, bothfixed plates and movable plates have a rectangular form, although fixedplates 7, 7, . . . have lateral projections 7b', 7b', . . . which cometo engagement with horizontal grooves provided on the inner side wallsof casing 1 to block vertical movement of the fixed plates. It may beapparent that the fixed plates are laterally deflectable as movableplates 6, 6, . . . As seen from FIG. 7d, fixed plates 7, 7, . . . have acut-off area on the upper portion thereof designed to avoid contactbetween the guide pin 2m and the fixed plates. All the space withincasing 1 is filled with viscous fluid A.

Now suppose that movable shaft 2 of FIG. 4a is pulled upward by anexternal force, suspended movable plates 6, 6, . . . are also movedupward linearly. Then thanks to the alignment effect, the clearancesbetween adjacent plates of movable plates 6, 6, . . . and fixed plates7, 7, . . . tend to be equalized and total effective length H of thedamper, or the distance betweeen two bearing piece 2k, 2k , in FIG. 4a,is equally divided by movable plates, 6, 6, . . . and fixed plates 7, 7,. . . so that an evenly distributed viscous drag against shearing forceis generated in the viscous fluid filling the space within the damper.Referring to the embodiment illustrated in FIGS. 6a and 6b which isdesigned to achieve the second object of the invention, a cylindricalcasing 1 comprises a bottom wall 1a, through which rotatably runs rotaryshaft 2 along the vertical axis of the damper, and an upper screw nutportion 1e, into which a cap plate 3 is screwed. Said rotary shaft 2carries a pivotable arm 4 at its lower end, which is rigidly fitted tothe rotary shaft by a holder screw 5. The casing 1 has vertical grooves1d, 1d, . . . symmetrically arranged on its inner side wall.

The space within the casing 1 is filled with viscous fluid A and thecasing is sealed by the cap plate 3. A number of movable discs 6, 6, . .. and fixed discs 7, 7, . . . are arranged vertically alternativelyarranged. Whereas, if the rotary shaft is rotated, the movable disc 6rotates with the shaft because the disc has notches 6b, 6b around acentral opening 6a which is engaged with vertical ridges 2d, 2d, . . .of the rotary shaft 2, fixed disc 7 can not rotate since it is held bythe casing 1 as a result of the coordinated effect of circular opening7a, peripheray projections 7b, 7b, . . . and vertical ridges 1d, 1d, . .. of the casing 1. It may be apparent that both the movable disc 6 andthe fixed disc 7 can shift their vertical position as in the case of theembodiments related with the first object of the invention. An adjusterscrew 8a screwed into a shaft bearing bore 3a of the cap plate 3 can beoperated from outside for vertical adjustment. A pusher disc 8b isplaced on the top of rotary shaft 2 and immediately below the cap plate3 and its central projection 8b is accommodated in the central boreformed on the bottom of the adjuster screw 8a in such a manner that bydriving the screw back and forth, the pusher disc 8b is moved back andforth, which in turn alters the total effective length of the damperdefined by the distance between the bottom wall 1a of the casing and thepusher disc 8b. Said adjuster screw 8a and pusher disc 8b constituteadjuster member 8. Reference symbols 8b", 8b", . . . in FIGS. 6a and 6bdenote so many projections provided on the periphery of the pusher disc8b to be engaged with vertical grooves 1d, 1d, . . . of the casing 1 toblock turning movement of the pusher disc 8b.

When a damper having a configuration as described above is used as adoor check, an external turning fore applied to the pivotable arm 4 isreceived the damper so that all the clearances between the adjacentmovable and fixed discs tend to be equalized and the total effectivelength H is evenly divided by the discs which become parallel to eachother.

Now suppose that the damping force of the damper has to be altered. Suchalteration can be realized by turning the adjuster screw 8a. If theadjuster screw 8a is turned to move forward to reduce the value of H andhence the distance between any two adjacent discs, the total viscousdrag of the viscous fluid is increased to enhance the effect of thedamper against the external force applied to the arm. The adjuster screw8a can be driven forward even if the casing 1 is completely filled withviscous fluid A so long as the fluid has the physical property of beingcompressible. If the fluid is not compressible, a layer of air formed onthe top of the fluid can accomodate the downward movement of the pusherdisc 8b.

Referring now to FIGS. 9a and 9b which show another embodiment toachieve the second object of the invention, this embodiment differs fromthat of FIGS. 6a and 6b in that a rotary shaft 2 does not pass throughthe bottom wall 1a but its cap disc 3 as in the case of the embodimentsdescribed in reference to the first object of the invention. Instead,the bottom of the rotary shaft 2 is accommodated in bearing recess 1b ofthe bottom wall 1a. The rotary shaft 2 has a flange 2a on the upperportion thereof from which a squared top portion 2c extends upward topass through a cap disc 3. A threaded bore 2b is axially formed in thetop portion 2c.

A square hole 4a of a pivotable arm 4 is fitted onto squared top portion2c that projects from cap disc 3 and rigidly held by a lock bolt 5screwed into threaded bore 2b. The pivotable arm 4 is subjected toexternal force.

In the embodiment, an adjuster member 8 is actually an adjuster screwbolt 8c screwed into a threaded bore vertically formed at an eccentricposition of the bottom wall 1c of the casing 1. The top end of the screwbolt 8c abuts the lower surface of the lowermost fixed disc 7 at aposition close to the inner wall surface 1c of the casing 1.

With such an arrangement, when the adjuster screw bolt 8c is drivenupward, said lowermost fixed disc 7 is pushed up to take a tiltedposture and as a result the distance between the disc and the movabledisc 6 located immediately above it is decreased to reduce overalleffective length H of the damper and hence increase the viscous dragagainst shearing force to the desired degree.

Referring to FIG. 7 which illustrates an embodiment designed to achievethe third object of the invention, this embodiment differs from that ofFIGS. 6a and 6b mentioned above, in that, unlike the above embodiment,this embodiment is provided a source of resilient force 9 which servesto effectively restore total effective length H of the damper once it isreduced through operation of the adjuster member 8.

In this embodiment, source of resilient force 9 is realized by formingmovable discs 6, 6, . . . not as flat discs but as those having theshape of a truncated cone with height h as measured between centralopening 6a and outer circumference 6a. Movable discs 6, 6, . . . havingsuch a shape are then arranged in such a manner that every other disc isreversed and all the movable discs and fixed discs are vertically linedup alternatively.

With this embodiment, if adjuster screw bolt 8a is driven forward, thepusher disc 8b is pressed down to lower the uppermost movable disc 6,which in turn presses down the disc next to it and in this manner theeffect of lowering the adjuster bolt is transmitted to all the discs. Asa result, the distance between the two adjacent discs are reduced and,at the same time, truncated cone-shaped movable discs 6, 6, . . . areflattened to lose some of height h. However, when the adjuster screwbolt 8a is driven back, the resilient force which inherent in thetruncated cone-shaped movable discs serves to quickly restore theiroriginal posture.

While the source of resilient force imparted to movable disc 6 in thisembodiment, fixed disc 7 or both movable and fixed disc 7 may be utilizeto provide such resilient force in a similar manner.

FIGS. 8b and 8c show two alternative sources of the resilient force 9.In FIG. 8b, reversed truncated cone-shaped small disc spring member 9ahaving central opening with a diameter larger than that of centralopening 6a of movable disc 6 and that of circular opening 7a of fixeddisc 7 is used as a source of resilient force and placed betweenadjacent movable disc 6 and fixed disc 7 with central opening 9b fittedto rotary shaft 2. In FIG. 8c on the other hand, a coil spring 9c placedbetween adjacent movable discs at the circumferential area of thecentral opening 6a of movable disc 6 provides a source of resilientforce 9. In this case, the size of coil spring 9c is determined in sucha manner that it does not come into contact with the periphery ofcircular opening 7a of fixed disc 7 but adequately held by rotary shaft2.

While a small disc spring member 9a and a coil spring 9c provide sourcesof resilient force so that other components are not required to have aninherent resilient force to right itself, the overall effect using suchmembers is quite similar to the embodiments shown in FIGS. 7 and 8a.

Referring to FIGS. 10 and 11 that illustrate an embodiment to achievethe fourth object of the invention, a casing 1 comprises verticalgrooves 1d, 1d, . . . on the inner lateral surface while the lower endof a rotary shaft 2 runs through the bottom wall 1a and engagedtherewith by means of an O-ring 1f. A squared top portion 2c is providedon a flange 2a found at the upper portion of said rotary shaft 2 toproject upward.

A cap disc 3 screwed into the casing 1 has threaded bore 3a, into whicha shaft bearing connector 10 is screwed. The squared top portion 2c ofthe rotary shaft 2 is lodged in a shaft bearing hole 10a of saidconnector 10 with clearance 10b to accommodate an up and down movementthereof. The casing 1 is closed by the cap disc 3.

A squared top portion 10d provided on flange 10c of said shaft bearingconnector 10 projects out of the cap disc 3 to engage with a squaredhole 4a of the pivotable arm 4 which is subjected to external rotatingforce. A lock bolt 5 is screwed into a threaded bore 10e of a shaftbearing connector 10 to prevent an unintentional removal of thepivotable arm 4.

The lower end of the rotary shaft 2 that projects out of the casing 1 isrigidly connected with a stop bolt 12a from outside of a rotary adjuster12. On the other hand, the rotary adjuster 12 is connected with thecasing 1 as a threaded inner periphery 12b comes into engagement with athreaded outer periphery 7g of the casing 1 provided at the lower endthereof. With such an arrangement, the rotary shaft 2 can be moved upand down by driving the rotary adjuster 12 back and forth.

From the flange 2a of the rotary shaft 2 downward, a locking portion 2mand nonlocking portion 2n are successively formed on said rotary shaft2. In the embodiment illustrated in FIG. 11, a locking portion of therotary shaft 2 is realized by a number of teeth or vertical ridges 2p,2p, . . . formed on the periphery of said shaft 2. The locking portion2m has at its lower end a tapered area 2m', where each tooth or ridgegradually lose its height until it smoothly reaches a nonlocking portion2n.

The casing 1 which is closed by a cap disc 3 is filled with viscousfluid A and movable discs 6, 6, . . . and fixed discs 7, 7, . . . arearranged alternatively therein in the vertical direction.

Movable disc 6 and rotary shaft 2 are interlocked as the locking notches6b, 6b, . . . provided on the circumferential area of central opening 6aof disc 6 come into engagement with teeth or vertical ridges 2p, 2p, . .. of locking portion 2m of rotary shaft 2 so that the movable disc 6 isrotated in accordance with the rotary movement of the rotary shaft 2.Besides, movable disc 6 is axially deflectable or can shift its verticalposition as seen in FIG. 10.

Fixed disc 7 is provided with circular opening 7a at its centre andprojections 7b, 7b, . . . around the outer periphery so that, asmentioned above, it is not caused to have any rotary movement as aresult of the rotary movement of the adjacent movable discs, although itcan shift its axial position just like the movable disc 6.

If a damper having an arrangement as this embodiment is used as a doorcheck, the movable discs 6, 6, . . . rotate in accordance with themovement of the rotary shaft 2 when the latter is turned in response tothe external turning force applied to the pivotable arm 4. This movementin turn generates a viscous drag against shearing force in viscous fluidA found between movable discs 6, 6, . . . and fixed discs 7, 7, . . . .Then, due to the alignment effect, the movable discs 6, 6, . . . and thefixed discs 7, 7, . . . shift their vertical positions to becomeparallel to each other and evenly divide the total effective length H ofthe damper.

The overall damping effect of this damper can be adjusted by turning therotary adjuster 12. More specifically, FIG. 10 shows a state in whichtapered area 2m' is located close to tapered bore 1a' formed in bottomwall 1a of the casing 1. Now, if the rotary adjuster 12 is drivenupward, the tapered area 2m' is gradually moved up and away from thebottom wall 1a and consequently nonlocking portion 2n of the shaft ismoved into the casing 1. Then eventually the lowermost movable disc 6 incasing 1 comes off from the locking portion 2m to a position thatsurrounds the non-locking area 2n.

Under this condition, the rotary movement of the rotary shaft 2 is nottransmitted to said lowermost movable disc 6 and therefore excluded fromthe rest of the movable discs in the sense that it does not take part inthe function of generating visous drag against shearing force to, as aresult, decrement the overall damping effect of the damper.

If the rotary adjuster 12 is further driven up, eventually the nextmovable disc 6 also comes off from the locking portion 2n of the rotaryshaft 2 to further decrement the damping effect of the damper.

To the contrary, if the rotary adjuster 12 is driven back to move therotary shaft 2 downward, the movable discs 6, 6, . . . that have beendisengaged from the locking portion 2m come one by one back to theposition where notches 6b, 6b, . . . of central opening 6a of a restoredmovable disc 6 are engaged with teeth 2p, 2p, . . . of locking portion2m of the rotary shaft 2 to increment the damping effect of the damper,or the position as shown in FIG. 10.

FIGS. 12a, 12b, 13a and 13b illustrate two embodiments of the presentinvention designed to achieve the fifth object of the invention, whichhave basically a similar configuration as the embodiment shown in FIGS.1a through 1c with reference to the first object of the invention andhence similar components are indicated by identical reference symbols.However, this embodiment further comprises one or more deformable feelerelements 13 within a casing 1.

While the embodiment of FIGS. 12a and 13a has a deformable feelerelement 13 made of silicone rubber having the shape of a disc with alarge central bore 13a, the embodiment of FIGS. 12b and 13b contains adeformable feeler element 13 made of bimetal also having the shape of adisc with a large central bore 13a, which is warped into a dish-likeform when heated. A rotary shaft 2 runs idly through a central bore 13a.A deformable feeler element 13 may be located either on the bottom ofthe casing 1 between bottom wall 1a and the lowermost fixed disc 7 orbetween the lowermost fixed disc 7 and the fixed disc 7 next to it.Aternatively, the deformable feeler element 13 may be locatedimmediately under a cap disc 3 or between any arbitrarily selectedadjacent movable disc 6 and a fixed disc 7. Moreover, the number of thedeformable feeler element 13 is not necessarily limited to one but morethan one elements may be appropriately used at multiple locations withinthe casing.

It is well known that silicone rubber is deformed by the change of theambient temperature, expanding to increase its volume when the ambienttemperature rises and contracting to decrease its volume when thetemperature falls.

On the other hand, a deformable feeler element made of bimetal is warpedby temperature rise to take on a dish-like form, or a bowl-like form inan extreme case, so that, when heated, height S of the element definedby the vertical distance between central opening 13a and outercircumference 13b becomes significantly large.

Therefore, if said deformable feeler element 13 is provided within adamper, the element increases its thickness, in the case of siliconerubber, by the temperature rise as often observed in summer to push upthe lowermost fixed disc 7, which in turn moves the adjacent disc upwardso that eventually the total effective length H of the damper comprisingmovable disc 6, 6, . . . and the fixed disc 7, 7, . . . becomesdecreased.

Consequently, the clearance between any two adjacent discs is narrowedand therefore the reduction of viscosity of viscous fluid A due to thetemperature rise can be compensated by the increased drag againstshearing force due to the reduced clearance between the movable disc andthe fixed disc. Thus, a damper having a structure as that of thisembodiment can constantly maintain its desired damping effect regardlessof fluctuation of temperature all the year round.

FIGS. 14a through 15c illustrate three different embodiments of theinvention to achieve the sixth object of the invention. The arrangementof these embodiments is basically similar to that of the embodiment forthe first and the fourth objects and therefore similar components areindicated by identical reference symbols. Now the embodiment illustratedin FIGS. 14a and 15a is different from those embodiment only in that afixed disc 7 is realized by bonding two disc elements, each havingcentral circular opening 7a and projections 7b, 7b, . . . provided onthe outer periphery, with deformable feeler member 7e made of siliconerubber or a similar material sandwiched therebetween.

The embodiment illustrated in FIGS. 14b and 15 b comprises, as opposedto the above embodiment, a movable disc 6 realized by bonding two discelements together with a deformable feeler element 6j of silicone rubberor a similar material sandwiched therebetween and provided with a commoncentral opening 6a, while fixed disc 7 is a simple one-piece disc havinga central circular opening 7a and peripheral projections 7b, 7b, . . .

While in the above two embodiments, all the movable discs and fixeddiscs respectively have identical structures comprising deformablefeeler element 6j and 7e, it is possible to make them to haverespectively only part of the movable discs and the fixed disccomprising the deformable feeler elements 6j and 7e.

It is well known that silicone rubber is laterally deformed in responseto temperature change, increasing its volume as temperature rises anddecreasing its volume as temperature falls.

In the embodiment illustrated in FIGS. 14c and 15c, both or either andall or part of movable discs 6 and fixed discs are realized with thedeformable feeler element 6j or 7e contained therein. FIG. 14c shows astate where all the movable discs 2 have the form of flat disc which isperpendicular to a movable shaft 2. However, if temperature rises,movable discs 6, 6, . . . that contain bimetal are warped to take on adishlike shape to present a conical longitudinal sectional view andincrease the height, or the thickness, defined by the vertical distancebetween the central opening 6a and the outer periphery 6i.

Thus, if a multi-disc damper having a design as described above is usedas a door check and an external force is applied to a pivotable arm 4,it not only functions in the same manner as the embodiments realized forthe first object of the invention, but maintains total effective lengthH as all the discs keeps their parallel relationship.

With a damper having such a construction, where silicone rubber is usedfor deformable feeler element 6j and/or element 7e, the elementsincrease the thickness as temperature rises particularly in summer andin turn both or either of movable discs 6, 6, . . . and fixed discs 7,7, . . . increase the thickness to narrow the clearances between them.Consequently, if the viscosity of viscous fluid A is reduced to decreasethe overall drag effect of the damper as a result of temperature rise,the narrowed clearance tends to compensate the reduced viscous dragagainst shearing force and therefore maintain the drag effect at arequired level all the year round.

On the other hand, if bimetal is used for deformable feeler elements 6jor 7e, movable discs 6, 6, . . . or fixed discs 7, 7, . . . becomewarped to take on a dishlike form in response to the termperature riseto increase their effective thickness. Consequently, the clearancebetween the adjacent discs decrease to compensate the reduced drageffect as in the case of those using silicone rubber.

Referring to FIGS. 16 through 21b illustrating embodiments designed toachieve the seventh object of the invention, these embodiments differfrom those described in reference to the first object, in that they aredesigned to address the situation where they are subjected to externalresilient force B constantly applied to the movable discs 6, 6, . . .and the fixed discs 7, 7, . . . in the axial direction as schematicallyillustrated in FIGS. 21a and 21b. Thus, the embodiment illustrated inFIGS. 16 and 17 is provided with a compressed coil spring 14a receivedin a circular groove formed on the lower surface of a cap disc 3, saidspring 14a having its lower end pressed against the uppermost fixed disc7.

The embodiments respectively illustrated in FIGS. 18, 19 and 20 differfrom the above embodiment with regard to the manner of receivingexternal force and the way that bimetal is employed. This will bedescribed below.

While the embodiment of FIG. 16 has a spring coil as the source ofexternal force, the embodiment of FIG. 18 has a inversed trancatedconical-shaped spring 14b located between the cap disc 3 and theuppermost movable disc 6 as the source of resilient external force. Therest of the movable discs 6, 6, . . . are simple one-piece discs, whilefixed discs 7, 7, . . . are made of bimetal.

The embodiment of FIG. 19 has a compressed coil spring 14a received incircular groove 1h formed in bottom wall 1a of casing 1, said coilspring 14a having its upper end pressed against the lowermost fixed disc7 made of bimetal. In this embodiment, all the movable discs 6, 6, . . .and the fixed discs 7, 7, . . . are made of bimetal and therefore takeon a conical shape when ambient temperature falls.

The embodiment of FIG. 20 has movable discs 6, 6, . . . and compressedcoil spring 14a received by a circular groove 3b as the source ofresilient external force B as in the case of the embodiment of FIG. 16.However, this embodiment further comprises a circular elastic sheet 15of rubber arranged between said spring 14a and the uppermost fixed disc7. Said circular elastic sheet 15 is held at the edge of its inneropening between movable shaft 2 and the cap disc 3 and at the edge ofits outer periphery between the cap disc 3 and the casing 1.

Thus, if a multi-disc rotary damper having a structure as any one ofthese embodiments is used as a door check, it not only exerts itsdamping effect against the rotating external force applied to thepivotable arm 4, but also presents a feature of maintaining its dampingeffect at a required level all the year round in the manner as describedbelow.

FIG. 21a schematically illustrates the state of the inside of the damperwhen ambient temperature is relatively high as in summer and thereforeall the discs are found almost in parallel to each other. Now, ifambient temperature falls as in winter, both or either and all or partof the movable discs 6, 6, . . . and the fixed discs 7, 7, . . . made ofbimetal, whichever the case may be, come to be deformed to take on aconical shape, since the discs are so designed that the total effort ofthe deformed discs surpasses the resilient external force applied bycompressed coil spring 14 or some other means. FIG. 21b illustrates acase where movable discs 6, 6, . . . are made of bimetal and thereforethey take on a conical shape. Consequently, the distance between twoadjacent fixed discs varies from t1 or the value as shown in FIG. 21a tot2 or the value shown in FIG. 21b, shifting the total effective lengthfrom H1 to H2. Therefore, the average distance t between the adjacentmovable disc and the fixed disc is increased to offset the increase ofviscous drag against shearing force due to the increased viscosity ofviscous fluid A caused by the temperature fall in winter and thus theoverall damping effect of the damper will be maintained at a constantlevel.

Again in summer when ambient temperature rises, movable discs 6, 6, . .. return to a flat state and movable discs 6, 6, . . . as well as fixeddiscs 7, 7, . . . are pressed axially downward by resilient externalforce B to decrease the overall effective height of the damper from H2to H1 and distance t between two adjacent fixed discs from t2 to t1 sothat the state shown in FIG. 21b returns to the state shown in FIG. 21a.Under this condition, while viscous fluid A loses some of its viscositybecause of decline of temperature in winter, the loss is compensated bythe increased viscous drag against shearing force due to the narroweddistance between the adjacent discs.

POTENTIAL INDUSTRIAL APPLICATIONS

As described earlier, a damper according to the present invention andrealized to achieve the first object thereof has movable discs and fixeddiscs which are axially deflectable so that they can exploit thealignment effect highly advantageously to obtain a reliable viscous dragagainst shearing force without causing any significant local stress thatcan damage the components such as disc members and any rise of internalpressure of the viscous fluid contained within the damper. Because ofthese advantages, such a multi-disc damper can be manufactured at areasonably low cost.

If a damper having a stucture as described above is required to modifyits viscous drag against shearing effect, such modification can berealized by simply altering the number of discs used in the damperwithout necessity of replacing them with those of a different size.

A damper according to the present invention that achieves the secondobject thereof has, beside the features as described above withreference to the damper achieving the first object of the invention, afeature of modifying its viscous drag against shearing force by quicklyaltering the total effective length of the damper through simpleoperation of adjuster member from outside.

A damper according to the present invention and realized to achieve thethird object thereof further comprises a source of resilient force whichensures a minimum distance between the adjacent movable and fixed discsso as to completely eliminate a condition where viscous fluid becomesnonexistent between discs as a result of flow out of the fluid and henceno sufficient viscous drag can be generated when an external force isapplied to the damper. Because of said source of resilient force, adamper of this type affords quick and smooth modification including fineadjustment of its drag by means of an adjuster member.

A damper according to the present invention and realized to achieve thefourth object thereof has, beside the features of a damper describedwith reference to the first object of the invention, a feature ofmodifying the viscous drag against shearing force of the damper throughoperation of driving back and forth an adjuster screw to move up anddown the rotary shaft of the damper that can be conducted from outsidein a simple and quick manner which has not been possible to date.

A damper according to the present invention and realized to achieve thefifth object thereof has, beside the features described with referenceto the first and fourth objects of the invention, a feature of makingthe damper capable of maintaining a required level of drag regardless offluctuation of ambient temperature because of deformable feeler elementsit comprises beside said axially deflectable, movable and fixed discs.Therefore, if such a damper is used, a situation where a required dragagainst shearing force is not available will be completely eliminated.

A damper according to the present invention and designed to achieve thesixth object thereof comprises axially deflectable movable and fixeddiscs, all or part of which are made of a material which is deformed inresponse to temperature change with a view to eliminate a conditionwhere a required level of drag is not obtainable because of change ofambient temperature.

A damper according to the present invention and realized to achieve theseventh object thereof comprises axially deflectable movable and fixeddiscs made of bimetal which are constantly subjected to an externalforce. A damper having such a design can effectively maintain a requiredlevel of viscous drag against shearing force all the year round becausethe total effective axial length of the damper can be modified tosignificantly alter the distance between the adjacent discs. Such adamper is totally free from the drawbacks of conventional dampers.

What is claimed is;
 1. A multi-disc damper using viscous fluidcomprising within a casing a number of movable discs provided on arotary shaft capable of being rotated by external force so as to berotated with the shaft; a number of fixed discs not interlocked with therotary shaft for being free of rotary movement and arranged in analternating arrangement with the movable discs; a viscous fluid materialfilling the space between the movable and the fixed discs; wherein saidfixed discs are not rotatable around the rotary shaft due to engagementwith the casing but are axially deflectable and the movable discs arealso axially deflectable; and means, provided on said rotary shaft, foradjusting the overall drag of the damper; said adjusting meanssuccessively engaging, and thereby rotating, said movable discs so thatthe overall drag of the damper varies according to the number of movablediscs engaged.
 2. A multi-disc damper using viscous fluid comprisingwithin a casing a number of movable discs provided on a rotary shaftcapable of being rotated by external force so as to be rotated with theshaft, a number of fixed discs not interlocked with the rotary shaft forbeing free of rotary movement and arranged in an alternative arrangementwith the movable discs and a viscous fluid material filling the spacebetween the movable and the fixed discs, wherein said fixed discs arenot rotatable around the rotary shaft due to the engagement with thecasing but axially deflectable and the movable discs are also axiallydeflectable, said rotary shaft being provided with a locking portionhaving vertical ridges to be engaged with the movable discs to preventrotary movement thereof and a nonlocking portion passing through thecasing, the rotary shaft being made axially movable by means of a rotaryadjusting member provided on the casing and coupled to said nonlockingportion so that the nonlocking portion goes into or comes out of thecasing according to the axial movement of the rotary shaft in such amanner that the movable discs can come off from the locking portion oneby one starting from the one situated close to the nonlocking portion orinversely come into engagement with the locking portion in accordancewith the movement of the rotary shaft.
 3. A multi-disc damper usingviscous fluid according to claim 2, wherein the locking portion isformed in a number of vertical ridges provided around the peripheralsurface of the rotary shaft for engagement with the notches providedaround the central opening of the movable discs and said ridges aretapered at the lowest area thereof toward the nonlocking portion.